An experiment conducted by an online advertising firm has found that Donald Trump’s razor-thin 2016 election margin in Michigan could have been helped by outside forces who spent just $4 per voter to successfully sway the results.

While the research does not focus on Russia’s involvement in disrupting the election, it found that instigators relying on Facebook ads targeting persuadable voters could have swung enough votes to provide victory for Trump in Michigan on a budget of just $42,800. That is an astoundingly low level of strategic spending within a presidential campaign season.

As far back as March, research indicated that Michigan voters were swamped with pro-Trump or anti-Hillary Clinton propaganda on social media in the days leading up to the 2016 election.

In recent weeks, the story has unraveled quickly as news reports provide detailed information about Russian-based or Russian-backed fake news factories, including quotes from some of the operatives who strategically manipulated U.S. voters. Some reports indicate that the phony Russian content received 2.6 billion hits in the U.S.

What’s more, Facebook is under fire for failing to come clean on just how significant the social media network was in acting as enablers for the Russian efforts to make ridiculous political claims go viral.

Company executives will be testifying before two congressional committees next month to explain why thousands of political ads generated by Russia were sold on Facebook.

Business Insider has advanced the story by working with three digital advertising agencies who studied how easy it would have been to sway voters in Michigan and Wisconsin, which were both key to Trump’s November win. The emphasis was on logistics but the findings could certainly apply to Russian cyber warriors, or rogue agitators within the U.S.

One firm, Mediassociates, found that effective targeting of undecided voters in those two states would be fairly easy and inexpensive using Facbook’s advertising mechanisms, which can narrow the focus based on an audience’s demographics, geography, cultural preferences and political persuasion.

Much of this information is compiled based on what Facebook users read, and which posts earn “Likes.”

Here’s how Business Insider explained this experiment:

Mediassociates built a model based on a basic rule of thumb of digital advertising, which is that 1 out of 2,000 people (or 0.05%) who view an ad will respond or take action on the message. Their model works backwards from the exact numbers of people by which Trump won both Wisconsin and Michigan, although, in reality, it’s possible that someone targeting swing voters could try to reach more people than that and therefore might spend more money on their campaign.

Donald Trump won Michigan by 10,704 votes. So, assuming that only 0.05% viewers will react to an ad, a person would need to aim for about 21.4 million advertising impressions. Given that Facebook ads cost about $2.00 for every 1,000 impressions, Kunz’s team estimates that to sway about 10,700 voters you’d need a budget of $42,800 – about $4 per voter.

In Wisconsin, the numbers are very similar. Trump won the state by 22,748 votes. Using the same model described for Michigan, that would suggest a budget of $90,992 – again about four bucks apiece.

Another strategy consists of targeting ads to promote fake news content.

To be clear, this is not about what angle on a story is taken by an established news organization or whether a particular report is entirely accurate. This is about sites that report wild claims aimed at hapless voters.

The graph below shows examples of the fake news that received more online traffic in the final weeks of the 2016 presidential campaign than established media sources.

The power of Facebook in a volatile campaign environment was demonstrated by another digital marketing firm, MobileMonkey, which ran an experiment by creating a fake news website, a Facebook page for that website, and an ad to promote the page.

The result, within minutes of the launch, was an ad that reached 4,645 people, generating 44 “Likes,” 27 shares, 20 comments, three “Page Likes,” and approximately 200 website clicks. The cost for this fake news endeavor? $53.58.

“People like to think they can’t be persuaded, but the math says it works,” Mediassociates vice president Ben Kunz told Business Insider.

“… A clever political operator … for a few hundred grand, he or she could tip an entire presidential election.”